Grounding load estimation device, control device, and grounding load estimation method

ABSTRACT

The present invention achieves a technique that not only makes it possible to reduce sensor-related cost but also makes it possible to estimate a ground contact load of a vehicle with sufficiently high accuracy. A ground contact load estimation device ( 100 ) causes an acquisition section to acquire a physical quantity related to a vehicle, causes a reference inertia load calculation section ( 111 ) to calculate a reference inertia load with use of the physical quantity, uses the physical quantity to cause a correction value calculation section ( 112 ) to calculate an inertia load correction value, and causes an inertia load estimation section ( 110 ) to estimate an inertia load by adding the inertia load correction value to the reference inertia load.

This application is a Continuation of PCT International Application No.PCT/JP2019/028203 filed in Japan on Jul. 18, 2019, which claims thebenefit of Patent Application No. 2019-117696 filed in Japan on Jun. 25,2019, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a ground contact load estimationdevice, a control device, and a ground contact load estimation method.

BACKGROUND ART

Conventionally, a technique is known in which a ground contact load at awheel of a vehicle is estimated and a result of the estimation is usedto control a braking force and a driving force of the vehicle so as toenhance running stability of the vehicle. The ground contact load isrequired to be estimated with sufficiently high accuracy from theviewpoint of enhancing running stability of the vehicle. Examples of aknown technique for estimating the ground contact load include atechnique in which (i) a rolling angular speed detected by a rollingrate sensor and (ii) a pitching angular speed detected by a pitchingrate sensor are used to estimate a ground contact load (see, forexample, Patent Literature 1).

CITATION LIST Patent Literature

[Patent Literature 1]

Japanese Patent Application Publication Tokukai No. 2013-216278

SUMMARY OF INVENTION Technical Problem

However, such a conventional technique as described earlier requiresmore sensors that are necessary for estimation of the ground contactload, such as the rolling rate sensor and the pitching rate sensor. Thismay cause an increase in cost. The conventional technique thus still hasroom for consideration from the viewpoint of at least a reduction insensor-related cost.

An aspect of the present invention has an object to achieve a techniquethat not only makes it possible to reduce sensor-related cost but alsomakes it possible to estimate a ground contact load of a vehicle withsufficiently high accuracy.

Solution to Problem

In order to attain the object, a ground contact load estimation devicein accordance with an aspect of the present invention is a groundcontact load estimation device for estimating a ground contact load of avehicle, the ground contact load estimation device including: anacquisition section configured to acquire a physical quantity related tothe vehicle; and an inertia load estimation section including (i) areference inertia load calculation section configured to calculate areference inertia load with use of the physical quantity that has beenacquired by the acquisition section and (ii) a correction valuecalculation section configured to calculate an inertia load correctionvalue with use of the physical quantity that has been acquired by theacquisition section, the inertia load estimation section beingconfigured to estimate an inertia load by adding the inertia loadcorrection value to the reference inertia load.

Furthermore, in order to attain the object, a control device inaccordance with an aspect of the present invention is a control devicefor estimating a ground contact load acting on a vehicle, and directlyor indirectly using the ground contact load to control one or more otherdevices of the vehicle, the control device including: an acquisitionsection configured to acquire a physical quantity related to thevehicle; and an inertia load estimation section including (i) areference inertia load calculation section configured to calculate areference inertia load with use of the physical quantity that has beenacquired by the acquisition section and (ii) a correction valuecalculation section configured to calculate an inertia load correctionvalue with use of the physical quantity that has been acquired by theacquisition section, the inertia load estimation section beingconfigured to estimate an inertia load by adding the inertia loadcorrection value to the reference inertia load.

Moreover, in order to attain the object, a ground contact loadestimation method in accordance with an aspect of the present inventionis a ground contact load estimation method for estimating a groundcontact load of a vehicle, the ground contact load estimation methodcomprising the steps of: acquiring a physical quantity related to thevehicle; calculating a reference inertia load with use of the physicalquantity acquired; calculating an inertia load correction value with useof the physical quantity acquired; and estimating an inertia load byadding the inertia load correction value to the reference inertia load.

Advantageous Effects of Invention

An aspect of the present invention makes it possible to estimate aground contact load of a vehicle with sufficiently high accuracy withuse of a sensor that is widely used to control driving of the vehicle.It is therefore possible to reduce sensor-related cost and also estimatea ground contact load of a vehicle with sufficiently high accuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a functionalconfiguration of a ground contact load estimation device in accordancewith Embodiment 1 of the present invention.

FIG. 2 is a block diagram illustrating an example of a functionalconfiguration of an inertia load estimation section of Embodiment 1 ofthe present invention.

FIG. 3 is a block diagram illustrating an example of a functionalconfiguration of a reference inertia load calculation section ofEmbodiment 1 of the present invention.

FIG. 4 is a view for describing a physical quantity related to a rollingbehavior of a vehicle body.

FIG. 5 is a view for describing a physical quantity related to apitching behavior of a vehicle body.

FIG. 6 is a view for describing rolling angular acceleration around thecenter of gravity of a vehicle body.

FIG. 7 is a view for describing a turning radius of a vehicle.

FIG. 8 is a block diagram illustrating an example of a functionalconfiguration of a road surface load estimation section of Embodiment 2of the present invention.

FIG. 9 is a view for describing a physical quantity related to a wheelof a vehicle.

FIG. 10 is a view schematically illustrating an example of aconfiguration of a vehicle to which a ground contact load estimationdevice in accordance with an embodiment of the present invention isapplied.

DESCRIPTION OF EMBODIMENTS

According to an embodiment of the present invention, a ground contactload at a wheel of a vehicle is estimated with sufficiently highaccuracy with reference to a physical quantity of the vehicle whichphysical quantity can be acquired with use of a sensor that isordinarily used to carry out control for enhancing running stability ofthe vehicle. Note that the expression “with “reference” to a physicalquantity” is herein a general term for direct or indirect use of thephysical quantity and herein means direct and/or indirect use of thephysical quantity.

[Ground Contact Load Estimation Device]

A ground contact load estimation device of an embodiment of the presentinvention estimates a ground contact load of a vehicle. The groundcontact load estimation device includes an acquisition section and aninertia load estimation section.

[Acquisition Section]

The acquisition section is a device for acquiring a physical quantityrelated to a vehicle. The acquisition section supplies the physicalquantity to the inertia load estimation section (described later) and acorrection value calculation section (described later). Examples of theacquisition section include various sensors and a device for calculatingand outputting the physical quantity.

According to the present embodiment, a sensor can be a sensor that isordinarily used (hereinafter also referred to as a “universal sensor”)to carry out standard control in relation to running of a vehicle. Thesensor does not need to include a rolling rate sensor and a pitchingrate sensor. Examples of the sensor (universal sensor) serving as theacquisition section include a longitudinal acceleration sensor thatacquires longitudinal acceleration of the vehicle, a lateralacceleration sensor that acquires lateral acceleration of the vehicle, awheel speed sensor that acquires a wheel angular speed of the vehicle,and a turning information sensor that acquires turning information ofthe vehicle. Examples of the turning information sensor include a yawrate sensor and a steering angle sensor.

Examples of the above physical quantity include a value of thelongitudinal acceleration sensor, a value of the lateral accelerationsensor, a value of the wheel speed sensor, a value of the turninginformation sensor, a mass of the vehicle, a gravitational center heightof the vehicle, a rolling inertia moment, a pitching inertia moment, afront axle intercentroid distance of the vehicle, a rear axleintercentroid distance of the vehicle, a front tread length of thevehicle, and a rear tread length of the vehicle.

[Inertia Load Estimation Section]

The inertia load estimation section includes a reference inertia loadcalculation section and the correction value calculation section. Theinertia load estimation section estimates an inertia load by adding aninertia load correction value calculated by the correction valuecalculation section to a reference inertia load calculated by thereference inertia load calculation section. The inertia load means avariation in ground contact load due to an effect of turning of thevehicle and an effect of acceleration/deceleration of the vehicle. Thereference inertia load calculation section calculates the referenceinertia load with use of the physical quantity that has been acquired bythe acquisition section. The reference inertia load means a solution ofan equation described later and representing the inertia load of thevehicle. The inertia load correction value is a correction value forcorrecting the reference inertia load so as to reduce a differencebetween the reference inertia load and a true inertia load.

According to the present embodiment, the physical quantity that is usedto calculate the reference inertia load can be a physical quantity thatis acquired by a universal sensor (described earlier) and a physicalquantity that is specific to the vehicle. For example, the referenceinertia load calculation section can calculate the reference inertiaload at each wheel of the vehicle in accordance with a model of thevehicle with use of the value of the longitudinal acceleration sensor,the value of the lateral acceleration sensor, the mass of the vehicle,the gravitational center height of the vehicle, the rolling inertiamoment, the pitching inertia moment, the front axle intercentroiddistance of the vehicle, the rear axle intercentroid distance of thevehicle, the front tread length, and the rear tread length.

Note here that the “model of the vehicle” is a model for making itpossible to calculate the reference inertia load. The model can bedetermined as appropriate in accordance with a mathematical expressionfor calculating the reference inertia load. For example, the model ofthe vehicle can be a model of a solution of a motion equationrepresented by a linear system, the solution being obtained byapplication of a minimum norm solution.

The correction value calculation section calculates the inertia loadcorrection value with use of the physical quantity that has beenacquired by the acquisition section. The physical quantity that is usedby the correction value calculation section to calculate the inertiaload correction value can also be a physical quantity that is acquiredby a universal sensor and a physical quantity that is specific to thevehicle, as described earlier. For example, the correction valuecalculation section can calculate the inertia load correction value withuse of the mass of the vehicle, the gravitational center height of thevehicle, the value of the wheel speed sensor, the value of the turninginformation sensor, the rolling inertia moment, the front tread length,and the rear tread length. The value of the turning information sensorcan be suitably a value of the yaw rate sensor or a value of thesteering angle sensor.

[Road Surface Load Estimation Section]

The ground contact load estimation device of the present embodiment canhave a further configuration provided that effects of the presentinvention can be obtained. For example, the ground contact loadestimation device can further include a road surface load estimationsection configured to estimate a road surface load of the vehicle.

The road surface load means a variation in ground contact load due to aneffect of a road surface, such as unevenness of the road surface. Inorder to reduce cost of the acquisition section (e.g., a sensor) forestimation of the road surface load, the road surface load estimationsection is preferably configured to estimate the road surface load withuse of the physical quantity that is acquired by a universal sensor andthe physical quantity that is specific to the vehicle. Note, however,the configuration of the road surface load estimation section is notlimited to this. For example, the road surface load estimation sectionpreferably estimates the road surface load by multiplying a tireeffective radius variation (described below) by a first gain. In thiscase, the acquisition section (described earlier) preferably includes awheel speed sensor that acquires the wheel angular speed of the vehicle,and is preferably a device for acquiring the physical quantity includingthe wheel angular speed, a steady load of the vehicle, and an inertiaload of the vehicle.

The road surface load estimation section includes a first gaincalculation section and a tire effective radius variation calculationsection. The first gain calculation section calculates the first gainfrom at least the steady load of the vehicle and the inertia load of thevehicle. The first gain is, at least, a parameter indicative of rigidityof a wheel (e.g., a tire) of the vehicle. The first gain is a value thatis unique to a wheel. As described later, the first gain can be foundfrom an equation that substantially represents rigidity of the wheel towhich a specific ground contact load is applied.

The tire effective radius variation calculation section calculates thetire effective radius variation by multiplying a variation in wheelangular speed by a second gain. The tire effective radius variation is avalue that represents, with use of a variation in wheel speed, avariation in radius of a tire due to an influence of the road surface.The variation in wheel angular speed can be found with reference to aresult of detection by the wheel speed sensor. The variation in wheelangular speed only needs to substantially represent a variation in wheelangular speed which variation is caused during a step of estimating aground contact load, and can be an approximate value of the variation.

The second gain is a parameter for reducing an influence of thevariation in wheel angular speed on an estimation result. In general, inestimation of a state quantity of the vehicle (e.g., a ground contactload of the vehicle), a result of the estimation and an actual runningstate tend to differ more greatly as a condition concerning actualrunning of the vehicle further deviates from a predetermined conditionconcerning ordinary running of the vehicle. The second gain can bedetermined by deriving, through experiment or simulation, for example, asuitable numerical value such that an estimated value of the groundcontact load is substantially identical to an actual measured value ofthe ground contact load of the vehicle under various conditions that areassumed concerning running of the vehicle.

The road surface load estimation section can include a furtherconfiguration provided that the effects of the present embodiment can beobtained. For example, the road surface load estimation section canfurther include a second gain correction section.

The second gain correction section calculates a slip ratio-related valueof the vehicle from the value of the wheel speed sensor so as to correctthe second gain in accordance with at least the slip ratio-related valueand a jerk of the vehicle. In this case, the acquisition section furtheracquires the jerk of the vehicle. The jerk can be acquired by, forexample, an acceleration sensor.

[Method for Estimating Ground Contact Load]

According to the present embodiment, a ground contact load of a vehiclecan be estimated by a method including the steps of: acquiring aphysical quantity related to the vehicle; calculating a referenceinertia load with use of the physical quantity that has been acquired bythe acquisition section; calculating an inertia load correction valuewith use of the physical quantity that has been acquired by theacquisition section; and calculating an inertia load by adding theinertia load correction value to the reference inertia load. The methodfor estimating the ground contact load of the vehicle can be carried outwith use of the ground contact load estimation device (describedearlier).

According to the present embodiment, an estimated value of the groundcontact load of the vehicle is obtained by adding together (i) theinertia load that has been estimated by the inertia load estimationsection and (ii) the steady load of the vehicle. The steady load is aground contact load at 1 G of the vehicle. For example, the steady loadcan be a calculated value that is based on the mass of the vehicle, orcan be a constant that is specific to the vehicle. In a case where theground contact load estimation device further includes the road surfaceload estimation section, an estimated value of the ground contact loadof the vehicle can be obtained by adding together (i) the inertia loadthat has been estimated by the inertia load estimation section, (ii) theroad surface load that has been estimated by the road surface loadestimation section, and (iii) the steady load.

[Control Device]

A control device of an embodiment of the present invention estimates aground contact load acting on a vehicle, and directly or indirectly usesthe ground contact load to control one or more other devices of thevehicle. The control device of the present embodiment can be configuredas in the case of a publicly known device for controlling one or moredevices of the vehicle in accordance with a ground contact load, exceptthat the control device includes the ground contact load estimationdevice (described earlier). Note that a case where the ground contactload is indirectly used includes, for example, a configuration in whichthe ground contact load estimated is used to carry out furtherestimation and use a value of a result of the further estimation tocontrol the other device(s).

An embodiment of the present invention will be specifically describedbelow.

Embodiment 1: First Embodiment of Ground Contact Load Estimation Device

[Functional Configuration of Ground Contact Load Estimation Device]

FIG. 1 is a block diagram illustrating an example of a functionalconfiguration of a ground contact load estimation device in accordancewith Embodiment 1 of the present invention. As illustrated in FIG. 1, aground contact load estimation device 100 includes an inertia loadestimation section 110, a road surface load estimation section 120, alongitudinal acceleration sensor and lateral acceleration sensor(longitudinal and lateral acceleration sensor) 131, a steering anglesensor or yaw rate sensor (steering angle/yaw rate sensor) 132, a wheelspeed sensor 133, a steady load providing section 141, a delayingsection 142, and adding sections 143 and 144.

The longitudinal and lateral acceleration sensor 131, the steeringangle/yaw rate sensor 132, and the wheel speed sensor 133 are connectedto the inertia load estimation section 110. The longitudinal and lateralacceleration sensor 131 and the wheel speed sensor 133 are connected tothe road surface load estimation section 120. The longitudinal andlateral acceleration sensor 131, the steering angle/yaw rate sensor 132,and the wheel speed sensor 133 (i) provide a physical quantity relatedto a vehicle and to be acquired by the inertia load estimation section110 and (ii) serve as an acquisition section with respect to the inertiaload estimation section 110.

The inertia load estimation section 110 outputs a signal of a calculatedinertia load. The inertia load estimation section 110 is connected tothe adding section 143 via the delaying section 142. The steady loadproviding section 141 outputs a signal of a steady load. The steady loadproviding section 141 is also connected to the adding section 143. Theadding section 143 is connected to each of the adding section 144 andthe road surface load estimation section 120. The road surface loadestimation section 120 is connected to the adding section 144.

The longitudinal and lateral acceleration sensor 131, the steeringangle/yaw rate sensor 132, the wheel speed sensor 133, the steady loadproviding section 141, and the inertia load estimation section 110 (i)provide the physical quantity related to the vehicle and to be acquiredby the road surface load estimation section 120 and (ii) serve as anacquisition section with respect to the road surface load estimationsection 120.

Furthermore, the inertia load estimation section 110 and the roadsurface load estimation section 120 are each connected to a network of acontrol system of the vehicle (e.g., CAN (described later)), though notillustrated. The inertia load estimation section 110 and the roadsurface load estimation section 120 acquire, via such a network, thephysical quantity that is specific to the vehicle, such as a mass of thevehicle, a gravitational center height of the vehicle, a rolling inertiamoment measured with respect to a point on a road surface which pointcorresponds to the center of gravity of the vehicle, a pitching inertiamoment measured with respect to the point on the road surface, a frontaxle intercentroid distance, a rear axle intercentroid distance, a fronttread length, and a rear tread length. The network also corresponds toan acquisition section of Embodiment 1.

FIG. 2 is a block diagram illustrating an example of a functionalconfiguration of an inertia load estimation section of Embodiment 1 ofthe present invention. As illustrated in FIG. 2, the inertia loadestimation section 110 includes a reference inertia load calculationsection 111 and a correction value calculation section 112.

FIG. 3 is a block diagram illustrating an example of a functionalconfiguration of a reference inertia load calculation section ofEmbodiment 1 of the present invention. As illustrated in FIG. 3, thereference inertia load calculation section 111 includes a system matrixsection 301, an input matrix section 302, an adding section 303, and adelaying section 304. The system matrix section 301 is connected to theadding section 303, the adding section 303 is connected to the delayingsection 304, and the delaying section 304 is connected to the systemmatrix section 301. The input matrix section 302 is connected to anoutside, for example, the network (described earlier), and is connectedto the adding section 303.

The road surface load estimation section 120 is constituted by apublicly known device for estimating a road surface load. For example,the road surface load estimation section 120 is a device for estimatinga road surface load from, for example, an image that has been capturedby a camera (not illustrated).

[Logic of Estimation of Ground Contact Load]

A ground contact load of Embodiment 1 is represented by Equation (1)below. In Equation (1), F_(z0nom) represents the ground contact load ina 1 G state, dF_(z0,inertia) represents the inertia load, anddF_(z0,road) represents the road surface load. As described earlier, theinertia load means a variation in ground contact load due to an effectof turning of the vehicle and an effect of acceleration/deceleration ofthe vehicle, and the road surface load means a variation in groundcontact load due to an effect of a road surface, such as unevenness ofthe road surface.

F _(z0) =F _(z0nom) +dF _(z0,inertia) +dF _(z0,road)   (1)

FIG. 4 is a view for describing a physical quantity related to a rollingbehavior of a vehicle body. FIG. 5 is a view for describing a physicalquantity related to a pitching behavior of a vehicle body. FIG. 6 is aview for describing rolling angular acceleration around the center ofgravity of a vehicle body.

dF_(z0,inertia) is represented by three motion equations of Equations(2A), (2B), and (2C) below. Equation (2A) represents motion in avertical direction, Equation (2B) represents the rolling behavior, andEquation (2C) represents the pitching behavior. Regarding a position ofa wheel, the front, the rear, the right, and the left are hereinexpressed as “f”, “r”, “r”, and “l”, respectively.

Regarding a direction with respect to the vehicle, a longitudinaldirection, a lateral direction, and the vertical direction are expressedas “x”, “y”, and “z”, respectively.

dF _(z0fl) +dF _(z0fr) +dF _(z0rl) +dF _(z0rr) =ma _(z)   (2A)

t _(rf)(dF _(z0fl) −dF _(z0fr))+t _(rr)(dF _(z0rl) −dF _(z0rr))=(I _(x)+I ₁){dot over (p)}−ma _(y) h ₀   (2B)

−l _(f)(dF _(z0fl) +dF _(z0fr))+l _(r)(dF _(z0rl) −dF _(z0rr))=(I _(y)+I ₂){dot over (q)}+ma _(x) h ₀   (2C)

As illustrated in FIGS. 4 and 5, m represents the mass of the vehicle,ho represents the gravitational center height of the vehicle. a_(x)represents longitudinal acceleration of the vehicle. a_(y) representslateral acceleration of the vehicle. a_(z) represents verticalacceleration of the vehicle. I₁ and I₂ represent correction values forcalculating inertia moments around road surface points with use ofinertia moments around axes passing through respective centers ofgravity COG1 and COG2. The center of gravity COG1 represents a center ofgravity in the width direction of a vehicle body 200, and the center ofgravity COG2 represents a center of gravity in the longitudinaldirection of the vehicle body 200.

Furthermore, as illustrated in FIG. 4, (I_(x)+I₁) represents the rollinginertia moment around the road surface point, I_(x) represents theinertia moment around the rolling axis passing through the center ofgravity COG1, t_(rr) represents half the length of a rear tread of thevehicle (the rear tread length multiplied by ½), and t_(rf) representshalf the length of a front tread of the vehicle (the front tread lengthmultiplied by ½). Dotted p represents rolling angular accelerationaround the road surface point.

Moreover, as illustrated in FIG. 5, (I_(y)+I₂) represents the pitchinginertia moment around the road surface point, and I_(y) represents theinertia moment around the pitching axis passing through the center ofgravity COG2. l_(f) represents a longitudinal distance between thecenter of gravity COG2 and a front axle of the vehicle body 200, l_(r)represents a distance between the center of gravity COG2 and a rearaxle, and (l_(f)+l_(r)) represents a wheelbase. Dotted q representspitching angular acceleration around the road surface point.

Assuming that dF_(est) ^((k)) is a calculated value of the variation inground contact load at a given point in time, a vector thereof isrepresented by Equation (3) below. In the following Equation (3), krepresents the number of times of calculation.

{right arrow over (dF _(est) ^((k)))}={right arrow over (dF _(z0)^((k)))}=[dF _(z0fl) dF _(z0fr) dF _(z0rl) dF _(z0rr)]^(T)   (3)

A matrix into which Equations (2A) to (2C) are transformed isrepresented by Equation (4) below, and Equation (5) below is derivedfrom Equation (4). A 3×3 matrix on the right side of Equation (5) isalso referred to as a matrix K′, and a 3×1 matrix in parentheses on theright side of Equation (5) is also referred to as a matrix a′.

$\begin{matrix}{{\begin{bmatrix}1 & 1 & 1 \\{- t_{rf}} & t_{rr} & {- t_{rr}} \\{- l_{f}} & l_{r} & l_{r}\end{bmatrix}\begin{bmatrix}{dF}_{{z0}\;{fr}} \\{d\; F_{z\; 0{rt}}} \\{dF}_{z\; 0{rr}}\end{bmatrix}} = {\begin{bmatrix}{ma}_{z} \\{{\left( {l_{x} + l_{1}} \right)\overset{.}{p}} - {{ma}_{y}h_{0}}} \\{{\left( {l_{y} + l_{2}} \right)\overset{.}{q}} + {{ma}_{x}h_{0}}}\end{bmatrix} - {\begin{bmatrix}1 \\t_{rf} \\{- l_{f}}\end{bmatrix}{dF}_{z\; 0{fl}}}}} & (4) \\{\begin{bmatrix}{dF}_{z\; 0{fr}} \\{dF}_{z\; 0{rl}} \\{dF}_{z\; 0{rr}}\end{bmatrix} = {\begin{bmatrix}\frac{l_{r}}{l_{f} + l_{r}} & 0 & {- \frac{1}{l_{f} + l_{r}}} \\\frac{{l_{f}l_{rr}} + {l_{r}l_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & \frac{1}{2\; t_{rr}} & {- \frac{t_{rf} - t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}} \\\frac{{l_{f}t_{rr}} - {l_{r}t_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & {- \frac{1}{2\; t_{rr}}} & \frac{t_{rf} + t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}\end{bmatrix}\left( {\begin{bmatrix}{ma}_{z} \\{{\left( {l_{x} + l_{1}} \right)\overset{.}{p}} - {{ma}_{y}h_{0}}} \\{{\left( {l_{y} + l_{2}} \right)\overset{.}{q}} + {{ma}_{z}h_{0}}}\end{bmatrix} - {\begin{matrix}a^{\prime} \\\begin{bmatrix}1 \\t_{rf} \\{- l_{f}}\end{bmatrix}\end{matrix}{dF}_{z\; 0\;{fl}}}} \right)}} & (5)\end{matrix}$

Assuming here that “dF_(z0fl)” is “Z”, Equation (3) is represented byEquation (6) below. Z is a variable satisfying Equations (2A) to (2C). A4×1 matrix in the first term on the right side of Equation (6)represents a vector a. A 4×3 matrix in the second term on the right sideof Equation (6) is also referred to as a matrix K, and a 3×1 matrix inthat term is also referred to as a matrix U. The vector a is representedby a matrix of Equation (7) with use of the matrix K′ and the matrix a′in Equation (5). The matrix K in Equation (6) is represented by a matrixof Equation (8) with use of the matrix K′ in Equation (5).

$\begin{matrix}{\overset{\rightarrow}{{dF}_{est}^{(k)}} = {\begin{bmatrix}{dF}_{z\; 0\;{fl}} \\{dF}_{z\; 0\;{fr}} \\{dF}_{z\; 0\;{rl}} \\{dF}_{z\; 0{rr}}\end{bmatrix} = {{\underset{\overset{\rightarrow}{a}\;}{\begin{bmatrix}1 \\{- 1} \\{- \frac{t_{rf}}{t_{rr}}} \\\frac{t_{rf}}{t_{rr}}\end{bmatrix}}Z} + \underset{\overset{\rightarrow}{{dF}_{{est},p}}\;}{\underset{K}{\begin{bmatrix}0 & 0 & 0 \\\frac{l_{r}}{l_{f} + l_{r}} & 0 & {- \frac{1}{l_{f} + l_{r}}} \\\frac{{l_{f}t_{rr}} + {l_{r}t_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & \frac{1}{2\; t_{rr}} & {- \frac{t_{rf} - t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}} \\\frac{{l_{f}t_{rr}} - {l_{r}t_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & {- \frac{1}{2\; t_{rr}}} & \frac{t_{rf} + t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}\end{bmatrix}}\underset{U}{\begin{bmatrix}{ma}_{z} \\{{\left( {J_{z} + I_{1}} \right)\overset{.}{p}} - {{ma}_{z}h_{0}}} \\{{\left( {I_{y} + I_{2}} \right)\overset{.}{q}} + {{ma}_{z}h_{0}}}\end{bmatrix}}}}}} & (6) \\{\overset{\rightarrow}{a}\; = \begin{bmatrix}1 \\{{- K^{\prime}}a^{\prime}}\end{bmatrix}} & (7) \\{K = \begin{bmatrix}0 \\K^{\prime}\end{bmatrix}} & (8)\end{matrix}$

Assuming that a vector dF_(est,p) is the product of the matrix K and thematrix U on the right side of Equation (6), Equation (6) is representedby Equation (9) below. dF_(est,p) represents any solution of Equations(2A) to (2C). The motion equations (2A) to (2C) (described earlier) arethus represented by Equation (9). That is, the solution of the motionequations (2A) to (2C) is represented by a linear equation, and acalculated value of the ground contact load to be found is present inany of straight lines represented by the linear equation.

{right arrow over (dF _(est) ^((k)))}={right arrow over (dF_(est,p))}+{right arrow over (a)}Z   (9)

<Application of Minimum Norm Solution>

In the motion equations (2A) to (2C), there are four variables(dF_(z0fl), dF_(z0fr), dF_(z0rl), and dF_(z0rr)), and there are threeequations with respect to those variables. In view of this, a minimumnorm solution is applied to Equation (9). A condition represented byExpression (10) below, i.e., a value of a solution that is included insolutions of the motion equations and whose difference from a previouslycalculated value of the variation in ground contact load is minimized isdefined as the solution of Equation (9). In Expression (10), dF_(est)^((k−1)) represents the previously calculated value of the groundcontact load. dF_(est,p) represents any of the solutions of the motionequations.

Minimize∥{right arrow over (dF _(est) ^((k−1)))}−{right arrow over (dF_(est) ^((k)))}∥  (10)

Application of the above definition allows Equation (11) to be derivedfrom Equation (9) as shown below. In Equation (11), hatted a representsa unit vector of the vector a.

$\begin{matrix}\begin{matrix}{\overset{\rightarrow}{{dF}_{est}^{(k)}} = {\overset{\rightarrow}{{dF}_{{est},p}} + {\overset{\rightarrow}{a}\mspace{11mu} Z}}} \\{= {\overset{\rightarrow}{{dF}_{{est},p}} + {\frac{\overset{\rightarrow}{a}\mspace{11mu}}{\overset{\rightarrow}{a}}\left( {\left( {\overset{\rightarrow}{{dF}_{est}^{({k - 1})}} - \overset{\rightarrow}{{dF}_{{est},p}}} \right) \cdot \hat{a}} \right)}}} \\{= {\overset{\rightarrow}{{dF}_{{est},p}} + {\frac{\overset{\rightarrow}{a}\mspace{11mu}}{{\overset{\rightarrow}{a}}^{2}}\left( {\left( {\overset{\rightarrow}{{dF}_{est}^{({k - 1})}} - \overset{\rightarrow}{{dF}_{{est},p}}} \right) \cdot \overset{\rightarrow}{a}} \right)}}}\end{matrix} & (11)\end{matrix}$

<Linear Modeling>

Equation (11) that is expressed by a linear model is represented byEquation (12) below and is further represented by Equation (13).

$\begin{matrix}{\overset{\rightarrow}{{dF}_{est}^{(k)}} = {{\underset{A}{\left( \frac{{aa}^{T}}{{\overset{\rightarrow}{a}}^{2}} \right)}\overset{\rightarrow}{{dF}_{est}^{({k - 1})}}} + {\underset{B}{\left( {I - \frac{{aa}^{T}}{{\overset{\rightarrow}{a}}^{2}}} \right)K}U}}} & (12) \\{\overset{\rightarrow}{{dF}_{est}^{(k)}} = {{A\mspace{14mu}\overset{\rightarrow}{{dF}_{est}^{({k - 1})}}} + {B\mspace{11mu} U}}} & (13)\end{matrix}$

In the above equations, U represents an input value, A represents asystem matrix, and B represents an input matrix. The vector dF_(est,p)is represented by the product of the matrix K and the matrix U as shownbelow. The matrix K and the matrix U are represented as below, and A andB are each represented as below with use of a matrix.

$\overset{\rightarrow}{{dF}_{{est},p}} = {K\mspace{11mu} U}$$K = \begin{bmatrix}0 & 0 & 0 \\\frac{l_{r}}{l_{f} + l_{r}} & 0 & {- \frac{1}{l_{f} + l_{r}}} \\\frac{{l_{f}t_{rr}} + {l_{r}t_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & \frac{1}{2\; t_{rr}} & {- \frac{t_{rf} - t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}} \\\frac{{l_{f}t_{rr}} - {l_{r}t_{rf}}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}} & {- \frac{1}{2\; t_{rr}}} & \frac{t_{rf} + t_{rr}}{2\;{t_{rr}\left( {l_{f} + l_{r}} \right)}}\end{bmatrix}$ $U = \begin{bmatrix}{ma}_{z} \\{{\left( {I_{x} + I_{1}} \right)\hat{p}} - {{ma}_{y}h_{0}}} \\{{\left( {I_{y} + I_{2}} \right)\hat{q}} + {{ma}_{x}h_{0}}}\end{bmatrix}$$A = {\frac{{aa}^{T}}{{\overset{\rightarrow}{a}}^{2}} = {\frac{1}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)}\begin{bmatrix}t_{rr}^{2} & {- t_{rr}^{2}} & {{- t_{rf}}t_{rr}} & {t_{rf}t_{rr}} \\{- t_{rr}^{2}} & t_{rr}^{2} & {t_{rf}t_{rr}} & {{- t_{rf}}t_{rr}} \\{{- t_{rf}}t_{rr}} & {t_{rf}t_{rr}} & t_{rf}^{2} & {- t_{rf}^{2}} \\{t_{rf}t_{rr}} & {{- t_{rf}}t_{rr}} & {- t_{rf}^{2}} & t_{rf}^{2}\end{bmatrix}}}$$B = {{\left( {I - \frac{{aa}^{T}}{{\overset{\rightarrow}{a}}^{2}}} \right)K} = {\frac{1}{2}\begin{bmatrix}\frac{l_{r}}{l_{f} + l_{r}} & \frac{t_{rf}}{t_{rf}^{2} + t_{rr}^{2}} & \frac{- 1}{l_{f} + l_{r}} \\\frac{l_{r}}{l_{f} + l_{r}} & \frac{- t_{rf}}{t_{rf}^{2} + t_{rr}^{2}} & \frac{- 1}{l_{f} + l_{r}} \\\frac{l_{f}}{l_{f} + l_{r}} & \frac{t_{rr}}{t_{rf}^{2} + t_{rr}^{2}} & \frac{1}{l_{f} + l_{r}} \\\frac{l_{f}}{l_{f} + l_{r}} & \frac{- t_{rr}}{t_{rf}^{2} + t_{rr}^{2}} & \frac{1}{l_{f} + l_{r}}\end{bmatrix}}}$

The variable dF_(est) ^((k)) to be found can be acquired by substitutingthe matrix U in Equation (13) (described earlier), which is the linearmodel.

<Calculation of Correction Value>

The matrix U includes vertical acceleration a_(z), rolling angularacceleration dotted p, and pitching angular acceleration dotted q thatare not calculated from a detected value of the universal sensor(described earlier). A solution of Equation (13) can be found bysubstituting a predetermined value (e.g., zero) in these accelerations.Meanwhile, however, it is necessary to correct an influence of a_(z),dotted p, and dotted q.

“dF_(est) ^((k))” to be corrected is hereinafter also referred to as a“reference inertia load”, and a correction value for correcting theinfluence of a_(z), dotted p, and dotted q is hereinafter also referredto as an “inertia load correction value” and is represented by“dF_(Z0,corr)”. “dF_(Z0,inertia)”, which is an inertia load to be found,is represented by Equation (14) below. Note that an initial valuedF_(est) ⁽⁰⁾ of the reference inertia load is set to “0”.

{right arrow over (dF _(z0,inertia))}={right arrow over (dF _(est)^((k)))}+{right arrow over (dF _(z0,corr))}  (14)

(Correction of Influence of Rolling Angular Acceleration (Dotted p))

The inertia load correction value can be calculated from an appropriateequation corresponding to the extent and frequency of the influence ofa_(z), dotted p, and dotted q with use of a physical quantity that canbe acquired from the universal sensor. For example, the inertia loadcorrection value dF_(Z0,corr) is represented by Equation (15) below. InEquation (15), K_(p) represents an adjustment parameter, and ΣF_(y0)represents the sum total of tire lateral forces measured during rollingof the vehicle. A vector p is represented by Equation (16). A part(except ΣF_(y0)) of the right side of Equation (15) corrects theinfluence of dotted p and is important during turning of the vehicle.For example, K_(p) can be determined by (i) comparing (a) an actualmeasured value of the ground contact load of the vehicle that is turningwith (b) an estimated value of the ground contact load that is estimatedwith use of Equation (15) and (ii) setting K_(p) as appropriate so thatthe estimated value is substantially effective even under a conditionthat is extended from a running condition of the vehicle that has beensubjected to the measurement of the actual measured value.

$\begin{matrix}{\overset{\rightarrow}{{dF}_{{z\; 0},{corr}}} = {{{\Sigma\mathcal{F}}_{y\; 0} \cdot {K_{p}\left( \frac{h_{0}t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)}}\left( {1 + \frac{I_{1}}{I_{x}}} \right)\overset{\rightarrow}{p}}} & (15) \\{\overset{\rightarrow}{p} = \left\lbrack {\frac{t_{rf}}{t_{rr}} - {\frac{t_{rf}}{t_{rr}}\mspace{14mu} 1}\mspace{14mu} - 1} \right\rbrack^{T}} & (16)\end{matrix}$

Note here that the influence of dotted p which influence is expressed as“e dotted p” is represented by Equation (17) below. The left side ofEquation (17) is “e dotted p”, which is the influence of dotted p. The3×1 matrix by which B in Equation (17) is multiplied is a matrix inwhich a_(x), a_(y), a_(z), and dotted q are all set to zero in thematrix U (described earlier).

$\begin{matrix}{e_{\overset{.}{p}} = {{B\begin{bmatrix}0 \\{\left( {I_{x} + I_{1}} \right)\overset{.}{p}} \\0\end{bmatrix}} = {{\left( \frac{\left( {I_{x} + I_{1}} \right)t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)\overset{.}{p}\underset{\overset{\rightarrow\;}{p}}{\begin{bmatrix}\frac{t_{rf}}{t_{rr}} \\{- \frac{t_{rf}}{t_{rr}}} \\1 \\{- 1}\end{bmatrix}}} = {\left( \frac{\left( {I_{x} + I_{1}} \right)t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)\overset{.}{p}\overset{\rightarrow}{p}}}}} & (17)\end{matrix}$

Note here that FIG. 6 is a view for describing rolling angularacceleration around the center of gravity of a vehicle body. Asillustrated in FIG. 6, dotted p in FIG. 6 represents a rolling angularspeed around the center of gravity COG1 of the vehicle body. This dottedp around the center of gravity of the vehicle body is represented byEquation (18) below. The product of matrices on the right side ofEquation (18) is so minute as to be negligible and can therefore beregarded as zero.

$\begin{matrix}{{I_{x}\overset{.}{p}} = {{\Sigma\; F_{y\; 0}h_{0}} + {\left\lbrack {t_{rf}\mspace{14mu} - {t_{rf}\mspace{14mu} t_{rr}}\mspace{14mu} - t_{rr}} \right\rbrack\begin{bmatrix}F_{z\; 0{ft}} \\F_{z\; 0\;{fr}} \\F_{z\; 0{xl}} \\F_{z\; 0{rr}}\end{bmatrix}}}} & (18)\end{matrix}$

ΣF_(y0) is represented by Equation (19). Note here that FIG. 7 is a viewfor describing a turning radius with respect to an actual steering angleof a vehicle. FIG. 7 illustrates a case where the vehicle turns to theleft. FIG. 7 illustrates turning of the vehicle that is steered by frontwheels only. In FIG. 7, C is a turning center, and O is a wheel centralpoint. “R_(turn)” represents a turning radius and is a distance from theturning center C to a center of gravity COG3 of the vehicle.“R_(turn,l)” represents a distance from the turning center C in thewidth direction of the vehicle body to an intersection O of the wheel onthe left side of the vehicle, and “R_(turn,r)” represents a distancefrom the turning center C in the width direction of the vehicle body toan intersection O of the wheel on the right side of the vehicle. δ isthe actual steering angle.

A V_(fl) vector and a V_(fr) vector are travelling direction vectors atfront wheel points, and β_(fl) and β_(fr) are front wheel slip angles.β_(fl) is represented by an angle that is made by the V_(fl) vector withrespect to a line Lω_(fl), and β_(fr) is represented by an angle that ismade by the V_(fr) vector with respect to a line Lω_(fr). A broken lineLω_(fl) is a line extending in a rolling direction of the wheel and is astraight line passing through a center O_(fl) of the wheel. A brokenline Lω_(fr) is a line extending in the rolling direction of the wheeland is a straight line passing through a center O_(fr) of the wheel. AV_(rl) vector and a V_(rr) vector are travelling direction vectors atrear wheel points. β_(rl) and β_(rr) are rear wheel slip angles, and arerepresented by angles made by the V_(rl) vector and the V_(rr) vector,respectively, with respect to the longitudinal direction of the vehiclebody 200. In a case where the vehicle is steered by both the frontwheels and rear wheels, β_(fl) and β_(fr) are corrected as appropriatein consideration of steering by the rear wheels.

Given that “R_(turn)” in Equation (19) is represented by Equation (20),Equation (19) is represented by Equation (21). “R_(turn)” will bedescribed later. In Equation (21) below, “u” is an average of peripheralspeeds of all the wheels and is represented by Equation (22). InEquation (22), ω represents an angular speed of the wheel, and“R_(e,init)” represents an initial value of a tire effective radius. “δ”is represented by Equation (23). In Equation (23), δs represents adetected value of the steering angle sensor, and k₆ represents asteering gear ratio.

$\begin{matrix}{{\Sigma\; F_{y\; 0}} = \frac{{mu}^{2}}{R_{turn}}} & (19) \\{R_{turn} \approx \frac{l_{f} + l_{r}}{8}} & (20) \\{{\Sigma\; F_{y\; 0}} = \frac{{mu}^{2}\delta}{l_{f} + l_{r}}} & (21) \\{u = {{avg}\left( {\omega\; R_{e.{init}}} \right)}} & (22) \\{\delta = {k_{\delta}\delta_{S}}} & (23)\end{matrix}$

Thus, assuming that the influence of dotted p is “e dotted p”, the “edotted p” is represented by the following Equation (24).

$\begin{matrix}\begin{matrix}{e_{\overset{.}{p}} = {\left( \frac{\left( {I_{x} + I_{1}} \right)t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)\overset{.}{p}\overset{\rightarrow}{p}}} \\{= {\left( \frac{\left( {I_{x} + I_{1}} \right)t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)\left( \frac{h_{0}}{I_{x}} \right)\Sigma\; F_{y\; 0}}} \\{= {\left( \frac{h_{0}t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)\left( {1 + \frac{I_{1}}{I_{x}}} \right)\Sigma\; F_{y\; 0}}}\end{matrix} & (24)\end{matrix}$

Equation (20) is described here. R_(turn,l) is represented by Equation(25). Similarly, R_(turn,r) is represented by

Equation (26).

(δ+β_(fl)−β_(rl))R _(turn,l)=(l _(f) +l _(r))   (25)

(δ+β_(fr)−β_(rr))R _(turn,r)=(l _(f) +l _(r))   (26)

It can be assumed that R_(turn) is sufficiently large as compared withthe wheelbase of the vehicle and that both β and δ are sufficientlysmall. R_(turn) is represented by Equation (27) with use of Equations(25) and (26). In a process of derivation of Equation (27), asrepresented by

Equation (28), the product of differences in β between the front andrear wheels is sufficiently small between the right and left wheels ofthe vehicle and can be regarded as zero. Furthermore, as represented byEquation (29), f (3) obtained by subtracting the sum of β of the rearwheels from the sum of β of the front wheels of the vehicle issufficiently small as compared with R_(turn) and can be regarded aszero. Thus, “R_(turn)” is represented by Equation (20) (describedearlier).

$\begin{matrix}\begin{matrix}{R_{turn} = \frac{R_{{turn},l} + R_{{turn},r}}{2}} \\{= {\frac{l_{f} + l_{r}}{2}\left( {\frac{1}{\delta + \beta_{fl} - \beta_{rl}} + \frac{1}{\delta + \beta_{fr} - \beta_{rr}}} \right)}} \\{= {\frac{l_{f} + l_{r}}{2}\left( \frac{\left( {{2\;\delta} + {f(\beta)}} \right.}{\delta^{2} + {\delta\left( {{f(\beta)} + {\left( {\beta_{fl} - \beta_{rl}} \right)\left( {\beta_{fr} - \beta_{rr}} \right)}} \right.}} \right)}} \\{= {\frac{l_{f} + l_{r}}{\delta}\left( \frac{\left( {\delta + \frac{f(\beta)}{2}} \right)}{\delta + {f(\beta)}} \right)}} \\{\approx \frac{l_{f} + l_{r}}{\delta}}\end{matrix} & (27) \\{{\left( {\beta_{fl} - \beta_{rl}} \right)\left( {\beta_{fr} - \beta_{rr}} \right)} \approx 0} & (28) \\{{f(\beta)} = {{\beta_{fl} + \beta_{fr} - \beta_{rl} - \beta_{rr}} \approx 0}} & (29)\end{matrix}$

In the above description, “R_(turn)” is expressed by the actual steeringangle δ. Note, however, that “R_(turn)” can also be suitably expressedwith use of a yaw rate instead of the actual steering angle δ.

[Estimation of Ground Contact Load]

The longitudinal and lateral acceleration sensor 131 detects and outputslongitudinal acceleration and lateral acceleration of the vehicle. The(steering angle/yaw rate sensor) 132 detects and outputs a steeringangle or a yaw rate of the vehicle. The wheel speed sensor 133 detectsand outputs a wheel speed of the wheels of the vehicle. Furthermore, thenetwork (described earlier) outputs various physical quantities relatedto the vehicle. The acquisition section (described earlier) thusacquires and outputs the physical quantity related to the vehicle.

The reference inertia load calculation section 111 calculates thereference inertia load dF_(est) ^((k)) with use of the physical quantitythat has been acquired by the acquisition section.

The correction value calculation section 112 calculates the inertia loadcorrection value dF_(Z0,corr) with use of the physical quantity that hasbeen acquired by the acquisition section. Specifically, the correctionvalue calculation section 112 calculates the inertia load correctionvalue for correcting the influence of dotted p during turning inaccordance with Equation (15) (described earlier).

The inertia load estimation section 110 obtains an estimated value of aninertia load dF_(Z0,inertia) by adding the inertia load correction valuecalculated by the correction value calculation section 112 to thereference inertia load calculated by the reference inertia loadcalculation section 111. Specifically, the inertia load estimationsection 110 obtains the estimated value of the inertia load inaccordance with Equation (14) (described earlier).

The inertia load estimation section 110 supplies the inertia loaddF_(Z0,inertia) to the delaying section 142. The delaying section 142outputs the inertia load, if necessary, by delaying the inertia load sothat the inertia load is output with appropriate timing in accordancewith the subsequent control. For example, the delaying section 142delays the inertia load so that the inertia load is synchronized with adelay in moving average process which delay occurs in the road surfaceload estimation section 120 (described later). The adding section 143combines the inertia load with a steady load F_(Z0nom) that has beensupplied from the steady load providing section 141. The sum of thesteady load and the inertia load is supplied to the road surface loadestimation section 120 and the adding section 144.

Meanwhile, the road surface load estimation section 120 outputs anestimated value of a road surface load. The road surface load estimationsection 120 can output the estimated value of the road surface load withreference to the sum of the steady load and the inertia load. In thiscase, the estimated value of the road surface load with reference to thesteady load and the inertia load is obtained.

The estimated value of the road surface load which estimated value hasbeen supplied from the road surface load estimation section 120 iscombined, by the adding section 144, with the above sum. In this case,the sum of the steady load, the inertia load, and the road surface loadis obtained as an estimated value Fz₀ of the ground contact load of thevehicle. [Effects]

In Embodiment 1, the physical quantity that can be acquired by theuniversal sensor is used to calculate the reference inertia load andcalculate the inertia load correction value. This makes it possible toreduce sensor-related cost. A comparison between (a) an actual measuredvalue of the ground contact load which actual measured value is foundwith use of a sensor, provided in the vehicle, for more directlydetecting the ground contact load and (b) an estimated value of theground contact load which estimated value is found in accordance withEmbodiment 1 shows that Embodiment 1 makes it possible to obtain theestimated value of the ground contact load F_(z0) o which estimatedvalue is so accurate as to substantially coincide with the actualmeasured value.

In Embodiment 1, it is possible to use a solution of a motion equationwhich solution is obtained by application of the minimum norm solution.Therefore, Embodiment 1 thus configured is more effective in estimationof the ground contact load with high accuracy and is also more effectivein making a correction that allows such estimation to be applied to awide range of running conditions of the vehicle.

In Embodiment 1, the road surface load is estimated with reference tothe steady load and the estimated inertia load. Therefore, Embodiment 1thus configured makes it possible to estimate the road surface load withhigher accuracy, as compared with a case where the road surface load isestimated without reference to the steady load and the estimated inertiaload.

Embodiment 2: Second Embodiment of Ground Contact Load Estimation Device

Another embodiment of the present invention will be described below.Note that for convenience, members having functions identical to thoseof the respective members described in Embodiment 1 are given respectiveidentical reference numerals, and a description of those members isomitted.

(Correction of Influence of a_(z), Dotted p, and Dotted q)

In Embodiment 2, an inertia load correction value dF_(Z0,corr) can berepresented by Equation (30) below. The first term in large parentheses(the product of K_(a) and a vector a) on the right side of Equation (30)corrects an error of each of a_(z), dotted p, and dotted q which erroris caused by a minimum norm solution. In Equation (30), the vector a isrepresented by Equation (31) below, and a vector p is represented byEquation (16) (described earlier).

$\begin{matrix}{\overset{\rightarrow}{{dF}_{{z\; 0},{corr}}} = {\Sigma\;{F_{y\; 0}\left( {{K_{a}\overset{\rightarrow}{a}} + {{K_{p}\left( \frac{h_{0}t_{rr}}{2\left( {t_{rf}^{2} + t_{rr}^{2}} \right)} \right)}\left( {1 + \frac{I_{1}}{I_{x}}} \right)\overset{\rightarrow}{p}}} \right)}}} & (30) \\{\overset{\rightarrow}{a} = \left\lbrack {1\mspace{14mu} - 1\mspace{14mu} - {\frac{t_{rf}}{t_{rr}}\mspace{20mu}\frac{t_{rf}}{t_{rr}}}} \right\rbrack^{\gamma}} & (31)\end{matrix}$

In Equation (30), K_(a) is an adjustment parameter. K_(a) can bedetermined by comparing an estimated value obtained by Equation (30)with an actual measured value and setting K_(a) as appropriate so thatthe estimated value is substantially identical to the actual measuredvalue in estimation of a ground contact load of a vehicle.

[Estimation of Ground Contact Load]

A longitudinal and lateral acceleration sensor 131 detects and outputslongitudinal acceleration and lateral acceleration of the vehicle. A(steering angle/yaw rate sensor) 132 detects and outputs a steeringangle or a yaw rate of the vehicle. A wheel speed sensor 133 detects andoutputs a wheel speed of wheels of the vehicle. Furthermore, a network(described earlier) outputs various physical quantities related to thevehicle. An acquisition section (described earlier) thus outputs aphysical quantity related to the vehicle.

A reference inertia load calculation section 111 calculates a referenceinertia load dF_(est) ^((k)) with use of the physical quantity that hasbeen acquired by the acquisition section. Specifically, the referenceinertia load calculation section 111 calculates, in accordance withEquation (13) (described earlier), the reference inertia load as asolution to which the minimum norm solution is applied. For example, asystem matrix section 301 supplies, to an adding section 303, theproduct of a matrix A (described earlier) and a previously calculatedvalue of a ground contact load dF_(est) ^((k−1)), and an input matrixsection 302 supplies, to the adding section 303, the product of a matrixU (described earlier) and a matrix B. The adding section 303 combinesthese products so as to calculate the reference inertia load. Thereference inertia load is supplied from the reference inertia loadcalculation section 111. A delaying section 304 (i) adjusts timing sothat the reference inertia load to be supplied to the system matrixsection 301 has a previously calculated value in the next calculation ofthe reference inertia load and (ii) outputs the reference inertia loadthat has been received by the delaying section 304.

A correction value calculation section 112 calculates the inertia loadcorrection value dF_(Z0,corr) with use of the physical quantity that hasbeen acquired by the acquisition section. Specifically, the correctionvalue calculation section 112 calculates, in accordance with Equation(30), the inertia load correction value that corrects an influence ofdotted p, a_(z), and dotted q.

An inertia load estimation section 110 obtains an estimated value of aninertia load dF_(Z0,inertia) by adding the inertia load correction valuecalculated by the correction value calculation section 112 to thereference inertia load calculated by the reference inertia loadcalculation section 111. Specifically, the inertia load estimationsection 110 obtains the estimated value of the inertia load inaccordance with Equation (14) (described earlier).

The inertia load estimation section 110 supplies the inertia loaddF_(Z0,inertia) to a delaying section 142. The delaying section 142outputs the inertia load, if necessary, by delaying the inertia load sothat the inertia load is output with appropriate timing in accordancewith the subsequent control. For example, the delaying section 142delays the inertia load so that the inertia load is synchronized with adelay in moving average process which delay occurs in a road surfaceload estimation section 120 (described later). An adding section 143combines the inertia load with a steady load F_(Z0nom) that has beensupplied from a steady load providing section 141. The sum of the steadyload and the inertia load is supplied to the road surface loadestimation section 120 and an adding section 144.

Meanwhile, the road surface load estimation section 120 outputs anestimated value of a road surface load. The road surface load estimationsection 120 can output the estimated value of the road surface load withreference to the sum of the steady load and the inertia load. In thiscase, the estimated value of the road surface load with reference to thesteady load and the inertia load is obtained.

The estimated value of the road surface load which estimated value hasbeen supplied from the road surface load estimation section 120 iscombined, by the adding section 144, with the above sum. In this case,the sum of the steady load, the inertia load, and the road surface loadis obtained as an estimated value Fz₀ of the ground contact load of thevehicle.

According to Embodiment 2, the road surface load is estimated asdescribed below. The following description will discuss a functionalconfiguration and a logic of estimation of the road surface load inEmbodiment 2.

[Functional Configuration of Road Surface Load Estimation Section]

FIG. 8 is a block diagram illustrating an example of a functionalconfiguration of a road surface load estimation section of Embodiment 2.According to Embodiment 2, the road surface load estimation section 120has a tire effective radius variation calculation section 121, a firstgain calculation section 122, and a second gain correction section 123(see FIG. 8).

[Logic of Estimation of Road Surface Load]

A non-linear tire characteristic of the wheels of the vehicle islinearly approximated and is represented by Equations (51) and (52)below. In Equation (52), “F_(z0)” is the sum of the steady load and theinertia load as represented by Equation (53).

dF _(z0,road) =−a ₁ dR _(e)   (51)

a₁ =a ₁₁ F _(z0) +a ₁₂   (52)

F _(z0) =F _(z0nom) +dF _(z0,inertia)   (53)

In the above equations, a₁ represents a first gain, a₁₁ represents afirst parameter, and a₁₂ represents a second parameter.

The first gain a₁ indicates rigidity of a wheel of the vehicle. Thefirst gain a₁ is represented by a spring constant in a relationship ofthe spring constant to a ground contact load of a tire. The relationshipis represented by a non-linear curve, but can be approximated to alinear expression as represented by Equation (52).

The first parameter a₁₁ and the second parameter a₁₂ are both adjustmentparameters for applying the first gain a₁ to a wide range of conditions.The first parameter is represented by a slope of the linear expressionobtained by the approximation described above, and the second parameteris represented by an intercept of the linear expression.

FIG. 9 is a view for describing a physical quantity related to any wheelof a vehicle. In FIG. 9, R_(e) represents an effective radius of thetire, ω represents an angular speed of the wheel, and u₀ represents awheel center point speed parallel to a road surface. In consideration ofa slip ratio of the tire, the effective radius R_(e) is represented byEquation (54) below. Equation (55) below is derived from a totaldifferential of Equation (54).

$\begin{matrix}{R_{e} = {\frac{u_{0}}{\omega}\left( {1 + s} \right)}} & (54) \\{\frac{{dR}_{e}}{R_{e}} = {\frac{{du}_{0}}{u_{0}} + \frac{ds}{1 + s} - \frac{d\;\omega}{\omega}}} & (55)\end{matrix}$

Assume that the slip ratio does not change. In this case, Equation (56)is derived from Equation (55), and Equation (57) is further derived. InEquation (57), a₂ represents a second gain. The second gain a₂ is aparameter for adjusting an influence of a variation in wheel angularspeed on an estimation result. For example, the second gain can bedetermined by (i) comparing an actual measured value and an estimatedvalue of the ground contact load of the vehicle which is running under acondition in which the wheel angular speed changes and (ii) setting thesecond gain as appropriate so that the estimated value is substantiallyequally effective against various running conditions.

$\begin{matrix}{\frac{{dR}_{e}}{R_{e}} = {{\frac{{du}_{0}}{u_{0}} - \frac{d\;\omega}{\omega}} = {{\frac{d\;\omega}{\omega}\left\lbrack {\frac{{du}_{0} \times \omega}{u_{0} \times d\;\omega} - 1} \right\rbrack} = {{\frac{d\;\omega}{\omega}\left\lbrack {{\frac{{du}_{0}}{R_{e} \times d\;\omega}\left( {1 + s} \right)} - 1} \right\rbrack} = {\frac{d\;\omega}{\omega} \times a_{2}}}}}} & (56) \\{{dR}_{e} = {a_{2}{R_{e}\left( \frac{d\;\omega}{\omega} \right)}}} & (57)\end{matrix}$

dω/ω in parentheses in Equation (57) can be approximated as representedby Equation (58). In Equation (58), “movavg(ω)” represents a movingaverage of the wheel angular speed. Thus, Equation (59) is derived fromEquation (57).

$\begin{matrix}{\frac{d\;\omega}{\omega} \approx \frac{\omega - {{movavg}(\omega)}}{{movavg}(\omega)}} & (58) \\{{dR}_{e} = {a_{2}{R_{e}\left( \frac{\omega - {{movavg}(\omega)}}{{movavg}(\omega)} \right)}}} & (59)\end{matrix}$

Equation (60) is derived by substituting Equation (59) in Equation (51).The road surface load is calculated from Equation (60). Equation (60)includes movavg(co).

$\begin{matrix}{{dF}_{{z\; 0},{road}} = {{- a_{1}} \times a_{2} \times {R_{e}\left( \frac{\omega - {{movavg}(\omega)}}{{movavg}(\omega)} \right)}}} & (60)\end{matrix}$

The second gain a₂ can be represented by Equation (61) below. InEquation (61), a₂₁ represents a third parameter. The third parameter a₂₁is an adjustment parameter that is similar to the second gain. InEquation (61), the third parameter results in the same as the secondgain.

a₂=a₂₁   (61)

The second gain can be expressed with use of not only the thirdparameter but also a further correction value for correcting aninfluence of a specific vehicle state on the tire. For example, thesecond gain can be represented by Equation (62).

a ₂ =a ₂₁×

_(s)×

_(jerk)   (62)

In Equation (62), F_(s) represents a correction value for correcting aninfluence of the slip ratio, and F_(jerk) represents a correction valuefor correcting an error caused by a jerk. In this case, the thirdparameter is an adjustment parameter for reducing an influence of acorrection, made with use of these correction values, during running ofthe vehicle under a condition that is different from a running conditionwhich is to be corrected with use of the correction values. F_(s) andF_(jerk) each can increase and decrease (i) a calculated value of a slipratio-related value which calculated value is calculated by the secondgain correction section (described later) or (ii) an acquired value ofthe jerk which acquired value is acquired by the acquisition section, orcan substantially clear the calculated value or the acquired value inaccordance with a predetermined threshold. In order to make such acorrection, it is possible to calculate the road surface load fromEquation (63).

$\begin{matrix}{{dF}_{{z\; 0},{road}} = {{- a_{1}} \times a_{21} \times \mathcal{F}_{S} \times \mathcal{F}_{jerk} \times {R_{e}\left( \frac{\omega - {{movavg}(\omega)}}{{movavg}(\omega)} \right)}}} & (63)\end{matrix}$

[Estimation of Road Surface Load]

The first gain calculation section 122 of the road surface loadestimation section 120 calculates the first gain a₁ with use of at leastthe steady load and the inertia load. The first gain a₁ is representedby rigidity (a spring constant) of a wheel (tire) of the vehicle asdescribed earlier, and can be represented by a linear expression that isapproximate to a non-linear curve of the spring constant with respect tothe ground contact load. Here, the ground contact load is the sum of thesteady load and the inertia load as described earlier. The first gaincalculation section 122 substitutes the above sum in Equation (52) so asto calculate the first gain.

The second gain correction section 123 further acquires the jerk of thevehicle from the acquisition section. Specifically, the second gaincorrection section 123 acquires the jerk of the vehicle via a networksuch as CAN.

The second gain correction section 123 also calculates the slipratio-related value of the vehicle from a value of the wheel speedsensor. Specifically, the second gain correction section 123 acquires anumerical value corresponding to F_(s) in Equation (62).

Furthermore, the second gain correction section 123 corrects the secondgain in accordance with at least the slip ratio-related value and thejerk. The second gain is assumed to be set as the adjustment parameteras described earlier. Specifically, the second gain correction section123 (i) determines, in accordance with Equation (62), F_(s) and F_(jerk)that reduce an influence of the slip ratio and the jerk, and (ii) usesF_(s) and F_(jerk) to correct the second gain in accordance withEquation (62).

In a case where a change in slip ratio-related value is considered tohave a great influence on the estimation result, it is possible to setF_(s) so as to adjust such an influence. For example, F_(s) is acoefficient by which the slip ratio-related value is multiplied. In acase where the slip ratio-related value is less than a predeterminedvalue, F_(s) can be 0. In a case where the slip ratio-related value isnot less than the predetermined value, F_(s) can be 1 so that the slipratio-related value is adopted.

In a case where a change in jerk is considered to have a great influenceon the estimation result, it is possible to set F_(jerk) so as to adjustsuch an influence. For example, F_(jerk) is a coefficient by which thejerk acquired is multiplied. In a case where the jerk is more than apredetermined value, F_(jerk) can be 0. In a case where the jerk is notmore than the predetermined value, F_(jerk) can be 1 so that the jerkacquired is adopted.

As represented by Equation (62), the second gain correction section 123calculates the second gain that has been corrected by multiplying F_(s)and F_(jerk) by the third parameter. The third parameter a₂₁ in Equation(61) and the third parameter a₂₁ in Equation (62) can be identical to ordifferent from each other.

The tire effective radius variation calculation section 121 calculatesthe tire effective radius variation by multiplying a variation in wheelangular speed by the second gain. The variation in wheel angular speedis a numerical value including a variation value dω of the wheel angularspeed ω. Specifically, the tire effective radius variation calculationsection 121 calculates the tire effective radius variation bymultiplying the terms (except a₁) on the right side of Equation (60).

The road surface load estimation section 120 estimates the road surfaceload by multiplying, by the first gain, the tire effective radiusvariation that has been calculated by the tire effective radiusvariation calculation section 121. Specifically, the road surface loadestimation section 120 obtains an estimated value of the road surfaceload, in accordance with Equation (60), by multiplying the tireeffective radius variation by the first gain.

The ground contact load estimation device 100 obtains an estimated valueof the ground contact load F_(z0) of the vehicle by adding together (i)the steady load, (ii) the inertia load that has been estimated by theinertia load estimation section 110, and (iii) the road surface loadthat has been estimated by the road surface load estimation section 120.

[Effects]

Embodiment 2 further brings about the effects below in addition to theeffects of Embodiment 1 described earlier. According to Embodiment 2, itis possible to (i) estimate the road surface load of the vehicle withhigher accuracy. Furthermore, by including such an estimated value ofthe road surface load, it is possible to estimate the ground contactload of the vehicle with much higher accuracy. Moreover, by correctingthe second gain in accordance with a change in acceleration/decelerationof the wheel, it is possible to estimate the road surface load with muchhigher accuracy.

Embodiment 3: Embodiment of Control Device for Suspension

The following description will discuss an example in which a physicalquantity estimation device in accordance with Embodiment 3 is applied toa control device for controlling a suspension of a vehicle. Note thatfor convenience, members having functions identical to those of therespective members described in Embodiments 1 and 2 are given respectiveidentical reference numerals, and a description of those members isomitted.

A control device in accordance with Embodiment 3 (i) estimates a groundcontact load acting on the vehicle that has the suspension and (ii)controls a damping force of the suspension in accordance with the groundcontact load. The control device of Embodiment 3 can be configured as inthe case of a publicly known control device of a suspension except thatthe control device of Embodiment includes a ground contact loadestimation device (described earlier) and controls the damping force ofthe suspension in accordance with the ground contact load that has beenestimated by the ground contact load estimation device.

FIG. 10 is a view schematically illustrating an example of aconfiguration of a vehicle that has the ground contact load estimationdevice described above. As illustrated in FIG. 10, a vehicle 900includes a suspension 150, a vehicle body 200, wheels 300, a vehiclespeed sensor 450 that detects a vehicle speed (V), an engine 500, and anelectronic control unit (ECU) 600. The ECU 600 corresponds to aprocessor (described earlier) and includes the ground contact loadestimation device (described earlier).

Note that alphabets A to E in the reference signs each represent aposition in the vehicle 900. A represents a left front position in thevehicle 900, B represents a right front position in the vehicle 900, Crepresents a left rear position in the vehicle 900, D represents a rightrear position in the vehicle 900, and E represents a rear position inthe vehicle 900.

Furthermore, the vehicle 900 has various sensors such as a longitudinalacceleration sensor 340 that detects acceleration in the longitudinaldirection of the vehicle 900. Such a sensor corresponds to a universalsensor (described earlier). The vehicle 900 has a storage medium. Thestorage medium stores various pieces of information necessary forestimation of a physical quantity. Examples of such information includevarious physical quantities related to the vehicle, such as a wheelradius and a mass (vehicle weight) of the vehicle.

Via a controller area network (CAN) 370, respective output values of thevarious sensors are supplied to the ECU 600, and control signals aretransmitted from the ECU 600 to respective sections. It is possible tonewly provide the sensors in order to estimate the physical quantity(described later). However, from the viewpoint of cost, the sensors arepreferably sensors that already exist in the vehicle 900.

According to Embodiment 3, the damping force of the suspension iscontrolled in accordance with an estimated value of the ground contactload of the vehicle which estimated value is as accurate as an actualmeasured value of the ground contact load of the vehicle. This makes itpossible to sufficiently enhance running stability of the vehiclewithout the need to use any special sensor that is different from theuniversal sensor.

In Embodiment 3, the ground contact load that has been estimated in thecontrol device is directly used to control the damping force of thesuspension of the vehicle. According to an aspect of the presentinvention, the ground contact load thus estimated can be used to controlvarious devices of the vehicle as in the case of the suspension.Examples of such devices include not only an ordinary suspension butalso an electronically controlled suspension, a steering device, and anelectronically controlled driving force transmission device. The groundcontact load estimated can be used to control one or more of thesedevices of the vehicle. In control of these devices, an estimationresult of the ground contact load can be used directly as in Embodiment3 or indirectly to control those devices. Indirect use of the estimationresult of the ground contact load is, for example, to convert theestimation result to another state quantity so as to use an estimatedvalue of the state quantity obtained by the conversion to control theother device(s). By using the estimated value of the ground contact load(described earlier) to control the other device(s), as in the case ofEmbodiment 3, it is possible to sufficiently or further enhance runningstability of the vehicle without the need to use any special sensor thatis different from the universal sensor.

[Software Implementation Example]

Control blocks of the ground contact load estimation device 100(particularly, the inertia load estimation section 110 and the roadsurface load estimation section 120) can be realized by a logic circuit(hardware) provided in an integrated circuit (IC chip) or the like orcan be alternatively realized by software.

In the latter case, the ground contact load estimation device 100includes a computer that executes instructions of a program that issoftware realizing the foregoing functions. The computer not onlyincludes, for example, at least one processor but also includes acomputer-readable storage medium in which the program is stored. Anobject of the present invention can be achieved by the processor readingand executing, in the computer, the program stored in the storagemedium. Examples of the processor include a central processing unit(CPU).

Examples of the storage medium encompass “a non-transitory tangiblemedium” such as not only a read only memory (ROM) but also a tape, adisk, a card, a semiconductor memory, and a programmable logic circuit.The computer may further include a random access memory (RAM) or thelike in which the program is loaded.

The program can be made available to the computer via any transmissionmedium (such as a communication network or a broadcast wave) whichallows the program to be transmitted. Note that an aspect of the presentinvention can also be achieved in the form of a computer data signal inwhich the program is embodied via electronic transmission and which isembedded in a carrier wave.

The present invention is not limited to the embodiments, but can bealtered by a skilled person in the art within the scope of the claims.The present invention also encompasses, in its technical scope, anyembodiment derived by combining technical means disclosed in differingembodiments.

[Variation]

In an aspect of the present invention, a ground contact load can befound by, for example, a method disclosed in paragraph [0151] ofJapanese Patent Application Publication Tokukai No. 2008-074184.

In Embodiment 1 (described earlier), the members that are different fromthe inertia load estimation section 110 can be omitted as appropriate inaccordance with accuracy with which the ground contact load is expectedto be estimated. For example, it is possible to omit the road surfaceload estimation section 120 and the adding section 144 in Embodiment 1.In this case, the sum of the steady load and the inertia load is theestimated value of the ground contact load.

In Embodiment 2 (described earlier), part of the members can be omittedas appropriate in accordance with accuracy with which the ground contactload is expected to be estimated. For example, in Embodiment 2, it ispossible to omit the second gain calculation section in a case where thesecond gain is not corrected.

Alternatively, it is possible to omit or integrate part of calculationprocesses as appropriate in order to achieve, for example, a simplercalculation process. For example, the road surface load can becalculated in Embodiment 2 by (i) finding a value obtained bymultiplying the first gain a₁ and the second gain a₂ and (ii) applying aresultant gain value to, for example, Equation (60) (described earlier).

Aspects of the present invention can also be expressed as follows:

As is clear from the above description, a ground contact load estimationdevice (100) of an embodiment of the present invention is a groundcontact load estimation device for estimating a ground contact load of avehicle (900), the ground contact load estimation device including: anacquisition section configured to acquire a physical quantity related tothe vehicle; and an inertia load estimation section (110) including (i)a reference inertia load calculation section (111) configured tocalculate a reference inertia load with use of the physical quantitythat has been acquired by the acquisition section and (ii) a correctionvalue calculation section (112) configured to calculate an inertia loadcorrection value with use of the physical quantity that has beenacquired by the acquisition section, the inertia load estimation sectionbeing configured to estimate an inertia load by adding the inertia loadcorrection value to the reference inertia load.

The configuration not only makes it possible to reduce sensor-relatedcost but also makes it possible to estimate a ground contact load of avehicle with sufficiently high accuracy.

According to an embodiment of the present invention, the acquisitionsection can acquire, as the physical quantity, a value of a longitudinalacceleration sensor (131) that acquires longitudinal acceleration of thevehicle, a value of a lateral acceleration sensor (131) that acquireslateral acceleration of the vehicle, a value of a wheel speed sensor(133) that acquires a wheel angular speed of the vehicle, a value of aturning information sensor that acquires turning information of thevehicle, a mass of the vehicle, a gravitational center height of thevehicle, a rolling inertia moment, a pitching inertia moment, a frontaxle intercentroid distance of the vehicle, a rear axle intercentroiddistance of the vehicle, a front tread length of the vehicle, and a reartread length of the vehicle. Furthermore, the reference inertia loadcalculation section can calculate the reference inertia load inaccordance with a model of the vehicle with use of the value of thelongitudinal acceleration sensor, the value of the lateral accelerationsensor, the mass of the vehicle, the gravitational center height of thevehicle, the rolling inertia moment, the pitching inertia moment, thefront axle intercentroid distance of the vehicle, the rear axleintercentroid distance of the vehicle, the front tread length, and therear tread length. Moreover, the correction value calculation sectioncan calculate the inertia load correction value with use of the mass ofthe vehicle, the gravitational center height of the vehicle, the valueof the wheel speed sensor, the value of the turning information sensor,the rolling inertia moment, the front tread length, and the rear treadlength.

The configuration makes it possible to acquire the physical quantitywith use of a universal sensor or estimate the ground contact load withsufficiently high accuracy in accordance with the physical quantity thatis specific to the vehicle.

According to an embodiment of the present invention, the model can be amodel of a solution of a motion equation represented by a linear system,the solution being obtained by application of a minimum norm solution.

The configuration makes it possible to obtain an estimated value of theground contact load in accordance with an appropriate motion equationand with use of a solution to which an appropriate correction has beenmade. The configuration is therefore more effective in order to obtain,with high accuracy, an estimated value of the ground contact load whichestimated value is applied to a wide range of running conditions of thevehicle.

According to an embodiment of the present invention, the turninginformation sensor can be a yaw rate sensor or a steering angle sensor(132).

The configuration is more effective in order to estimate the groundcontact load of the vehicle with high accuracy with use of the physicalquantity that is acquired with use of a universal sensor.

According to an embodiment of the present invention, the acquisitionsection can (i) include a wheel speed sensor that acquires the wheelangular speed of the vehicle and (ii) acquire the physical quantityincluding the wheel angular speed, a steady load of the vehicle, and aninertia load of the vehicle, and the ground contact load estimationdevice can further include a road surface load estimation section (120)configured to estimate a road surface load of the vehicle. The roadsurface load estimation section can include: a first gain calculationsection (122) configured to use at least the steady load of the vehicleand the inertia load of the vehicle to calculate a first gain indicativeof at least rigidity of a wheel (300) of the vehicle; and a tireeffective radius variation calculation section (121) configured tocalculate a tire effective radius variation by multiplying a variationin wheel angular speed by a second gain for reducing an influence of thevariation in wheel angular speed on an estimation result, and the roadsurface load estimation section can estimate the road surface load bymultiplying the tire effective radius variation by the first gain. Theground contact load estimation device can estimate the ground contactload of the vehicle by adding together (i) the inertia load that hasbeen estimated by the inertia load estimation section and (ii) the roadsurface load that has been estimated by the road surface load estimationsection.

The configuration makes it possible to acquire the physical quantitywith use of a universal sensor or estimate the road surface load of thevehicle with sufficiently high accuracy in accordance with the physicalquantity that is specific to the vehicle, and also to estimate theground contact load including such a road surface load and having higheraccuracy.

According to an embodiment of the present invention, the acquisitionsection can further acquire a jerk of the vehicle, and the road surfaceground contact load estimation section can further include a second gaincorrection section (123) configured to correct the second gain. Thesecond gain correction section can calculate a slip ratio-related valueof the vehicle from the value of the wheel speed sensor so as to correctthe second gain in accordance with at least the slip ratio-related valueand the jerk.

The configuration is more effective in order to estimate the roadsurface load with higher accuracy.

A control device of an embodiment of the present invention is a controldevice (ECU 600) for estimating a ground contact load acting on avehicle, and directly or indirectly using the ground contact load tocontrol one or more other devices of the vehicle. The control deviceincludes: an acquisition section configured to acquire a physicalquantity related to the vehicle; and an inertia load estimation sectionincluding (i) a reference inertia load calculation section configured tocalculate a reference inertia load with use of the physical quantitythat has been acquired by the acquisition section and (ii) a correctionvalue calculation section configured to calculate an inertia loadcorrection value with use of the physical quantity that has beenacquired by the acquisition section, the inertia load estimation sectionbeing configured to estimate an inertia load by adding the inertia loadcorrection value to the reference inertia load.

The configuration not only makes it possible to reduce sensor-relatedcost but also makes it possible to control the other device(s) thatcontrol(s) a driving state of the vehicle in accordance with the groundcontact load that has been estimated with sufficiently high accuracy.This makes it possible to sufficiently enhance running stability of thevehicle.

According to an embodiment of the present invention, the one or moreother devices can be one or more devices selected from the groupconsisting of an electronically controlled suspension, a steeringdevice, and an electronically controlled driving force transmissiondevice.

The configuration is more effective in order to enhance runningstability of the vehicle.

A ground contact load estimation method of an embodiment of the presentinvention is a ground contact load estimation method for estimating aground contact load of a vehicle, the ground contact load estimationmethod including the steps of: acquiring a physical quantity related tothe vehicle; calculating a reference inertia load with use of thephysical quantity acquired; calculating an inertia load correction valuewith use of the physical quantity acquired; and estimating an inertiaload by adding the inertia load correction value to the referenceinertia load.

The configuration not only makes it possible to reduce sensor-relatedcost but also makes it possible to estimate a ground contact load of avehicle with sufficiently high accuracy.

REFERENCE SIGNS LIST

100 Ground contact load estimation device

110 Inertia load estimation section

111 Reference inertia load calculation section

112 Correction value calculation section

120 Road surface load estimation section

121 Tire effective radius variation calculation section

122 First gain calculation section

123 Second gain correction section

131 Lateral acceleration sensor

132 Steering angle/yaw rate sensor

133 Wheel speed sensor

141 Steady load providing section

142, 304 Delaying section

143, 144, 303 Adding section

200 Vehicle body

300 Wheel

301 System matrix section

302 Input matrix section

340 Longitudinal acceleration sensor

450 Vehicle speed sensor

500 Engine

600 ECU

900 Vehicle

1. A ground contact load estimation device for estimating a groundcontact load of a vehicle, said ground contact load estimation devicecomprising: an acquisition section configured to acquire, as a physicalquantity related to the vehicle, a value of a longitudinal accelerationsensor that acquires longitudinal acceleration of the vehicle, a valueof a lateral acceleration sensor that acquires lateral acceleration ofthe vehicle, a value of a wheel speed sensor that acquires a wheelangular speed of the vehicle, a value of a turning information sensorthat acquires turning information of the vehicle, a mass of the vehicle,a gravitational center height of the vehicle, a rolling inertia moment,a pitching inertia moment, a front axle intercentroid distance of thevehicle, a rear axle intercentroid distance of the vehicle, a fronttread length of the vehicle, and a rear tread length of the vehicle; andan inertia load estimation section including (i) a reference inertiaload calculation section configured to calculate a reference inertiaload in accordance with a model of the vehicle with use of the value ofthe longitudinal acceleration sensor, the value of the lateralacceleration sensor, the value of the wheel speed sensor, the mass ofthe vehicle, the gravitational center height of the vehicle, the rollinginertia moment, the pitching inertia moment, the front axleintercentroid distance of the vehicle, the rear axle intercentroiddistance of the vehicle, the front tread length, and the rear treadlength, each of which has been acquired by the acquisition section, and(ii) a correction value calculation section configured to calculate aninertia load correction value with use of the mass of the vehicle, thegravitational center height of the vehicle, the value of the wheel speedsensor, the value of the turning information sensor, the rolling inertiamoment, the front tread length, and the rear tread length, each of whichhas been acquired by the acquisition section, the inertia loadestimation section being configured to estimate an inertia load byadding the inertia load correction value to the reference inertia load,the inertia load meaning a variation in ground contact load due to aneffect of turning of the vehicle and an effect ofacceleration/deceleration of the vehicle.
 2. The ground contact loadestimation device as set forth in claim 1, wherein the model is a modelof a solution of a motion equation represented by a linear system, thesolution being obtained by application of a minimum norm solution. 3.The ground contact load estimation device as set forth in claim 1,wherein the turning information sensor is a yaw rate sensor or asteering angle sensor.
 4. The ground contact load estimation device asset forth in claim 1, wherein the acquisition section (i) includes awheel speed sensor that acquires the wheel angular speed of the vehicleand (ii) acquires the physical quantity including the wheel angularspeed, a steady load of the vehicle, and an inertia load of the vehicle,said ground contact load estimation device further comprising a roadsurface load estimation section configured to estimate a road surfaceload of the vehicle, the road surface load estimation section including:a first gain calculation section configured to use at least the steadyload of the vehicle and the inertia load of the vehicle to calculate afirst gain indicative of at least rigidity of a wheel of the vehicle;and a tire effective radius variation calculation section configured tocalculate a tire effective radius variation by multiplying a variationin wheel angular speed by a second gain for reducing an influence of thevariation in wheel angular speed on an estimation result, the roadsurface load estimation section estimating the road surface load bymultiplying the tire effective radius variation by the first gain, andthe ground contact load estimation device estimating the ground contactload of the vehicle by adding together (i) the inertia load that hasbeen estimated by the inertia load estimation section and (ii) the roadsurface load that has been estimated by the road surface load estimationsection.
 5. The ground contact load estimation device as set forth inclaim 4, wherein the acquisition section further acquires a jerk of thevehicle, the road surface load estimation section further includes asecond gain correction section configured to correct the second gain,and the second gain correction section uses the value of the wheel speedsensor to calculate a slip ratio-related value of the vehicle so as tocorrect the second gain in accordance with at least the slipratio-related value and the jerk.
 6. A control device comprising aground contact load estimation device recited in claim 1, said controldevice directly or indirectly using a ground contact load, estimated bythe contact load estimation device, to control one or more other devicesof the vehicle.
 7. The control device as set forth in claim 6, whereinthe one or more other devices are one or more devices selected from thegroup consisting of an electronically controlled suspension, a steeringdevice, and an electronically controlled driving force transmissiondevice.
 8. A ground contact load estimation method for estimating aground contact load of a vehicle, said ground contact load estimationmethod comprising the steps of: acquiring, as a physical quantityrelated to the vehicle, a value of a longitudinal acceleration sensorthat acquires longitudinal acceleration of the vehicle, a value of alateral acceleration sensor that acquires lateral acceleration of thevehicle, a value of a wheel speed sensor that acquires a wheel angularspeed of the vehicle, a value of a turning information sensor thatacquires turning information of the vehicle, a mass of the vehicle, agravitational center height of the vehicle, a rolling inertia moment, apitching inertia moment, a front axle intercentroid distance of thevehicle, a rear axle intercentroid distance of the vehicle, a fronttread length of the vehicle, and a rear tread length of the vehicle;calculating a reference inertia load in accordance with a model of thevehicle with use of the value of the longitudinal acceleration sensor,the value of the lateral acceleration sensor, the value of the wheelspeed sensor, the mass of the vehicle, the gravitational center heightof the vehicle, the rolling inertia moment, the pitching inertia moment,the front axle intercentroid distance of the vehicle, the rear axleintercentroid distance of the vehicle, the front tread length, and therear tread length, each of which has been acquired; calculating aninertia load correction value with use of the mass of the vehicle, thegravitational center height of the vehicle, the value of the wheel speedsensor, the value of the turning information sensor, the rolling inertiamoment, the front tread length, and the rear tread length, each of whichhas been acquired; and estimating an inertia load by adding the inertiaload correction value to the reference inertia load, the inertia loadmeaning a variation in ground contact load due to an effect of turningof the vehicle and an effect of acceleration/deceleration of thevehicle.
 9. The ground contact load estimation device as set forth inclaim 2, wherein the turning information sensor is a yaw rate sensor ora steering angle sensor.
 10. The ground contact load estimation deviceas set forth in claim 2, wherein the acquisition section (i) includes awheel speed sensor that acquires the wheel angular speed of the vehicleand (ii) acquires the physical quantity including the wheel angularspeed, a steady load of the vehicle, and an inertia load of the vehicle,said ground contact load estimation device further comprising a roadsurface load estimation section configured to estimate a road surfaceload of the vehicle, the road surface load estimation section including:a first gain calculation section configured to use at least the steadyload of the vehicle and the inertia load of the vehicle to calculate afirst gain indicative of at least rigidity of a wheel of the vehicle;and a tire effective radius variation calculation section configured tocalculate a tire effective radius variation by multiplying a variationin wheel angular speed by a second gain for reducing an influence of thevariation in wheel angular speed on an estimation result, the roadsurface load estimation section estimating the road surface load bymultiplying the tire effective radius variation by the first gain, andthe ground contact load estimation device estimating the ground contactload of the vehicle by adding together (i) the inertia load that hasbeen estimated by the inertia load estimation section and (ii) the roadsurface load that has been estimated by the road surface load estimationsection.
 11. The ground contact load estimation device as set forth inclaim 10, wherein the acquisition section further acquires a jerk of thevehicle, the road surface load estimation section further includes asecond gain correction section configured to correct the second gain,and the second gain correction section uses the value of the wheel speedsensor to calculate a slip ratio-related value of the vehicle so as tocorrect the second gain in accordance with at least the slipratio-related value and the jerk.
 12. A control device comprising aground contact load estimation device recited in claim 2, said controldevice directly or indirectly using a ground contact load, estimated bythe contact load estimation device, to control one or more other devicesof the vehicle.
 13. The control device as set forth in claim 12, whereinthe one or more other devices are one or more devices selected from thegroup consisting of an electronically controlled suspension, a steeringdevice, and an electronically controlled driving force transmissiondevice.
 14. The ground contact load estimation device as set forth inclaim 9, wherein the acquisition section (i) includes a wheel speedsensor that acquires the wheel angular speed of the vehicle and (ii)acquires the physical quantity including the wheel angular speed, asteady load of the vehicle, and an inertia load of the vehicle, saidground contact load estimation device further comprising a road surfaceload estimation section configured to estimate a road surface load ofthe vehicle, the road surface load estimation section including: a firstgain calculation section configured to use at least the steady load ofthe vehicle and the inertia load of the vehicle to calculate a firstgain indicative of at least rigidity of a wheel of the vehicle; and atire effective radius variation calculation section configured tocalculate a tire effective radius variation by multiplying a variationin wheel angular speed by a second gain for reducing an influence of thevariation in wheel angular speed on an estimation result, the roadsurface load estimation section estimating the road surface load bymultiplying the tire effective radius variation by the first gain, andthe ground contact load estimation device estimating the ground contactload of the vehicle by adding together (i) the inertia load that hasbeen estimated by the inertia load estimation section and (ii) the roadsurface load that has been estimated by the road surface load estimationsection.
 15. The ground contact load estimation device as set forth inclaim 14, wherein the acquisition section further acquires a jerk of thevehicle, the road surface load estimation section further includes asecond gain correction section configured to correct the second gain,and the second gain correction section uses the value of the wheel speedsensor to calculate a slip ratio-related value of the vehicle so as tocorrect the second gain in accordance with at least the slipratio-related value and the jerk.
 16. A control device comprising aground contact load estimation device recited in claim 9, said controldevice directly or indirectly using a ground contact load, estimated bythe contact load estimation device, to control one or more other devicesof the vehicle.
 17. The control device as set forth in claim 16, whereinthe one or more other devices are one or more devices selected from thegroup consisting of an electronically controlled suspension, a steeringdevice, and an electronically controlled driving force transmissiondevice.
 18. A control device comprising a ground contact load estimationdevice recited in claim 10, said control device directly or indirectlyusing a ground contact load, estimated by the contact load estimationdevice, to control one or more other devices of the vehicle.
 19. Thecontrol device as set forth in claim 18, wherein the one or more otherdevices are one or more devices selected from the group consisting of anelectronically controlled suspension, a steering device, and anelectronically controlled driving force transmission device.
 20. Acontrol device comprising a ground contact load estimation devicerecited in claim 14, said control device directly or indirectly using aground contact load, estimated by the contact load estimation device, tocontrol one or more other devices of the vehicle.